Multiple lumen catheters are commonly used to measure and monitor cardiac output. In operation, the catheter is typically introduced into a central vein of a patient and advanced toward the right atrium through the superior or inferior vena cava. Once the distal tip of the catheter is positioned within the vena cava, a small balloon positioned over the distal tip is inflated through an inflation lumen provided in the catheter. The balloon carries the catheter along the flow of blood through the right atrium and right ventricle into the main pulmonary artery. The catheter continues to advance until a wedge position is reached within an individual pulmonary artery wherein the balloon seals off the inflow of blood through the artery. In this position, pulmonary artery wedge pressure measurements are commonly taken and the balloon then deflated.
Subsequent to balloon deflation, thermodilution techniques are frequently utilized to measure cardiac output. Using thermodilution, a bolus of cold saline injectate is injected through a port in communication with one lumen of the catheter into the blood stream, and the resulting temperature change is measured with a thermistor located at a distal end of the catheter. Right heart ejection fraction can also be measured with thermodilution techniques in a known manner by further monitoring the occurrence of contractions using electrodes which are positioned at the distal end of the catheter within the right ventricle.
To achieve optimum accuracy using thermodilution techniques, the injectate is injected into the right atrium in an abrupt manner so as to be evenly distributed and well mixed in the right ventricle prior to ejection through the pulmonary artery. Commonly, the injectate is injected through a port located approximately 5 cm proximal of the tricuspid valve, adjacent the right atrium. When injected in this manner, the injectate flows countercurrent to the blood flow from the inferior vena cava, and thorough mixing with the incoming blood is achieved. Often, the injectate port comprises plural openings to further assist in injectate mixing and distribution within the blood stream.
Because heart size varies from patient to patient, the location of the injectate port once the distal tip of the catheter is positioned within the individual pulmonary artery also varies. Often, the catheter must be manually repositioned prior to thermodilution in order to locate the injectate port at the desired distance from the tricuspid valve. Then, once the thermodilution process has been completed, the catheter must be repositioned at the desired location within the pulmonary artery. This repositioning increases the risk of infection, the risk of damage to the heart and pulmonary artery caused by wall perforation, and further increases the amount of time that must be spent by the attending physician to perform the desired procedures.